In today's world of pneumatic operations, it is hard to imagine a time when air compressors were nonexistent in factories or workshops. The fact is, in the context of machine-age history, air compressors are a relatively recent innovation. Not long ago, the air tools used in workshops typically drew power from complex systems comprised of belts, wheels, and other large components. For the most part, such machinery was too massive, heavy, and costly for smaller operations, and was therefore confined primarily to larger companies.
Today, however, air compressors are usually found at factories where products are assembled or in most places where cars are serviced, such as gas stations and auto workshops. The list of tools that run on compressed air is long, but some of the most common pneumatic tools include the following: drills, grinders, nail guns, sanders, spray guns, and staplers. The most significant benefit of the standard workshop air compressor is its compact and relatively lightweight dimensions, which stand in contrast to centralized sources of power that generally utilize large motors. Additionally, air compressors last longer, require less maintenance, are easier to move from worksite to worksite, and are far less noisy than old-fashioned machinery.
Air compression is essentially a twofold process in which the pressure of air rises while the volume drops. In most cases, compression is accomplished with reciprocating piston technology, which makes up the vast majority of compressors on the market. Every compressor with a reciprocating piston has the following parts: crankshaft; connecting rod; cylinder; piston; and valve head.
Air compressors, for the most part, are powered by either gas or electric motors—it varies by model. At one end of the cylinder are the inlet and discharge valves. Shaped like metal flaps, the two valves typically appear at opposite sides of the cylinder's top end. During the “compression” process, what the piston effectively does with its back and forth movements is create a vacuum. As the piston retracts (i.e., on its down-stroke), the space in front gets filled with air, which is sucked through the inlets from the outside or from another gas source. When the piston extends (i.e., on its upstroke), that same air is compressed and therefore given the strength to push through the discharge valve—simultaneously holding the inlet shut—and into a tank or other compressed gas receptacle. As more air is sent into the tank, the pressure gains intensity.
In certain air compressor models, the pressure is produced with rotating impellers. However, the models that are typically used by mechanics, construction workers, and crafts people tend to run on positive displacement, in which air is compressed within compartments that reduce its space. Even though some of the smallest air compressors consist of merely a motor and pump, the vast majority have air tanks. The purpose of the air tank is to store amounts of air within specified ranges of pressure until it is needed to perform work. In turn, the compressed air is used to power the pneumatic tools connected to the unit supply lines. While all of this is going on, the motor repeatedly starts and stops to keep the pressure at a desired consistency.
In order to accommodate the vast range of pneumatic tools on the market, air compressors are manufactured in both one- and two-cylinder varieties. However, compressors used by private craftspeople and contractors often contain two-cylinders that function almost identically to single cylinders, the only real difference being that two strokes occur during each revolution. Some two-cylinder machines that are marketed to the public also work in two stages, where one piston sends compressed air to another cylinder for further compression.
For most single-stage air compressors, the preset pressure limit is set to a specific pressure per square inch (“psi”). When this limit is reached, a pressure switch goes off to stop the motor. In most operations, however, there is no need to even reach the pressure limit. For that reason, the compressor's air line is set to a regulator, where the user inputs the appropriate pressure level for a given tool. The regulator is bookended by two gauges: one that comes in front to monitor the pressure of the tank, and another gauge at the end to keep the pressure of the air line in check. Furthermore, the tank may be equipped with an emergency valve that triggers in the event of a mishap with the pressure switch. On some models, the switch might connect with an unloader valve, which can help reduce stress to the tank at times when the machine is deactivated.
For certain heavy-duty industrial operations, piston compressors are considered insufficient. In order to get the pressure intensity needed for complex pneumatic and other high-powered tools, professionals will generally opt for rotary screw air compressors. Unlike the piston air compressor, which relies on pulsation, the rotary screw air compressor produces an ongoing movement to generate power.
In a rotary screw compressor, air is compressed with a meshing pair of rotors. As the screws move in rotation, fluids gets sucked in, compressed, and ejected. In order to keep leakage rates at an absolute minimum, fast rotational rates are vital throughout the operation.
While compressors often are used to compress air from the atmosphere, compressors also can be used to compress other gases and liquids, or even combinations thereof. The type of gas/liquid compressed obviously is application dependent. Nevertheless, for applications that call for compressing gas/liquid that is dangerous or otherwise harmful to humans and/or the environment, additional care must be taken to prevent exposures, whether during normal operation or during compressor breakdown or failure. Such failure or breakdown can occur when any of the compressor components such as the crankshaft, connecting rod, cylinder, piston, rotor, or valve head fail in a manner that allows gas/liquid to escape to the atmosphere or open environment.
One precaution taken for dangerous gas/liquid applications is to enclose the compressor in an airtight enclosure so that any catastrophic failure to the compressor that might vent gas/liquid to the atmosphere is trapped in the enclosure. This has proven cumbersome and inefficient since it significantly adds to the size of the compressor unit, detracts from easy access to the compressor, and can hold too much heat. Accordingly, a better apparatus is needed for preventing gas/liquid exposures during compressor failure or breakdown.